In recent years, among intrinsic diseases that occur as age increases, brain diseases led by Alzheimer's disease have come to be great social problems. In the human brain, several tens of billions of neurons form complicated neurological circuits in which the terminal of a neurite of a neuron transmits information at the junctional portion called a synapse by the mediation of a neurotransmitter. Almost all brain disorders are considered to be caused by the destruction of neurological circuits due to degeneration or sloughing of neurons. As is widely accepted, neurons that have matured can no longer undergo cell division. Therefore, needless to say, damage to neurons considerably affects maintenance of brain functions.
Recently, substances that participate in differentiation and growth of nerve tissue have been searched for in the living body, and several in vivo hormones have already been clarified to be active substances.
However, it has been pointed out that these hormones disturb the in vivo hormone balance when used at a concentration where they exhibits their activity on neurons, and therefore in actual use they are problematic for administration. In view of the foregoing, there is a strong need for the development of extracorporeally derived pharmaceuticals that are effective in the prevention of damage to neurons, particularly prevention or treatment of degeneration and sloughing of neurons.
Accordingly, the object of the present invention is to provide a drug for treating brain diseases, which drug enables prevention or treatment of dementia and similar diseases caused by degeneration or sloughing of neurons.